A standard apparatus for extruding a thermoplastic laminate has a nozzle assembly whose body is centered generally on a plane and formed at the plane with a merge passage, with an outlet slot opening in one direction from the merge passage, with core-layer distribution and intake passages centered on the plane and opening in the opposite direction into the merge passage, and with cover-layer distribution and intake passages opening laterally into the merge passage. A core-layer fitting formed with tempering chambers forms part of the core-layer intake passage. A liquefied core-layer resin, for instance water-impervious PVDC, is fed under pressure to the core-layer intake passage and therethrough to the merge passage and outlet slot and a liquefied cover-layer resin is fed under pressure to the cover-layer intake passage and therethrough to the merge passage and outlet slot trimmings feed passage.
The core resin is normally very temperature sensitive and must also be at the same temperature as the other resins of the laminate to ensure good bonding therewith. In the known devices (PLASTICS WORLD August 1984, page 17) the bore of the nozzle body forms the core-resin intake passage and is fitted with a nickel sleeve. Plainly such a metal does not serve to isolate the heat of the stream entering. According to the temperature which the thermoplastifiable resin stream reaches for rheological reasons, the nozzle body gets so hot near the core-resin intake passage that the core resin can be overheated.
In order to avoid this it is known (see German Pat. No. 3,539,767) to form the core-resin intake passage in a fitting which is formed with tempering bores or chambers and which is set in a special seat in the nozzle body. In addition this fitting is formed with intake passages for the cover resins. Preferably the cover-resin intake passages extend along the full length of the tempering chambers.
While such arrangements are fairly effective, they are specifically adapted to only a certain type of operation. In a system where the cured sheet produced is trimmed, such an arrangement cannot make any use of the trimmings thus produced.